Isolator for alternator pulley

ABSTRACT

A decoupler for an alternator pulley in a serpentine drive system has a resilient, helical spring member that couples the alternator pulley with a hub structure through a spring retaining member. A bushing is disposed between the spring retaining member and the hub structure to facilitate sliding engagement therebetween. An annular sleeve member is disposed between the spring member and the alternator pulley to facilitate sliding engagement therebetween. The spring member is connected at one end thereof to the hub structure and connected at an opposite end thereof to the spring retaining member. The resilient spring member transmits the driven rotational movements of the alternator pulley by the serpentine belt to the hub structure such that the alternator shaft is rotated in the same direction as the alternator pulley while being capable of instantaneous relative resilient movements in opposite directions with respect to the alternator pulley during the driven rotational movement.

RELATED APPLICATION

This application claims priority to and all the benefits of U.S.Provisional Patent Application No. 60/373,327, filed on Apr. 18, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a decoupler and more particularly to analternator decoupler for a serpentine accessory drive systems forautomotive vehicles.

2. Description of Related Art

Serpentine accessory drive systems typically includes a driving pulleyon the output shaft of the internal combustion engine of the vehicle, aseries of driven pulleys for the accessories and a poly-V belt trainedabout the driving and driven pulleys. An advantage of the serpentinedrive is that, by providing an automatic belt tensioner on the belt, theaccessories can be fixedly mounted.

Particularly where the engine is of the four-cylinder type, the drivingpulley establishes a highly dynamic loading on the belt. This highdynamic loading is due to the variable torque output characteristics ofsuch engines. Under this circumstance, the tensioner cannot accommodateall of the variable torque characteristics. The result is sometimesnoise and decreased belt life due to instantaneous belt slippage. It hasbeen proposed to provide an engine crank shaft decoupler in order todeal with the high dynamic belt loading. This solution, while effective,is costly since the decoupler must have a capacity generally equal tothe system capacity.

It has also been proposed in U.S. Pat. No. 5,139,463 of common ownershipwith the present invention and which is hereby incorporated by referencein its entirety for its teachings as they relate to the presentinvention, to provide an alternator assembly wherein a coil spring isprovided between an alternator pulley and alternator hub structure fortransmitting the driven rotational movements of the alternator pulley bythe serpentine belt to the hub structure such that the alternatorarmature assembly is rotated in the same direction as the alternatorpulley while being capable of instantaneous relative resilientrotational movements in opposite directions with respect to thealternator pulley during the driven rotational movement thereof. Thishas proven to be a cost effective manner of accommodating high dynamicbelt loading to reduce noise and preserve belt life. Nevertheless, itcan be appreciated that the coil spring employed is subject tosignificant stresses over the life of the alternator. It is therefore anobject of the present invention to reduce stress on the spring andthereby increase the life thereof.

SUMMARY OF THE INVENTION

The above and related objects of this invention are realized byproviding a serpentine belt drive system for an automotive vehiclecomprising a drive assembly including an internal combustion enginehaving an output shaft with a driving pulley thereon rotatable about adriving pulley axis, a sequence of driven assemblies each having adriven pulley rotatable about an axis parallel with said driving pulleyaxis and a serpentine belt mounted in cooperating relation with saiddriving pulley and with said driven pulleys in a sequence whichcorresponds with the sequence of said driven assemblies when related tothe direction of movement of the belt to cause said driven pulleys torotate in response to the rotation of said driving pulley. The drivesystem further includes a sequence of driven assemblies including analternator assembly including a housing and an armature assembly mountedin the housing for rotation about an armature axis. A hub structure isfixedly carried by the armature assembly outwardly of the housing forrotation therewith about the armature axis. An alternator pulley ismounted on the hub structure for rotational movement about the armatureaxis. A coil spring resiliently couples the alternator pulley with thehub structure, the coil spring transmitting the driven rotationalmovements of the alternator pulley by the serpentine belt to the hubstructure such that the armature assembly is rotated in the samedirection as the alternator pulley while being capable of instantaneousrelative rotational movements in opposite direction with respect to thealternator pulley during the driven rotational movements thereof. Aninner spring engaging structure is rotationally fixed with respect tothe pulley and engages volutes of the coil spring as a result of radialcontraction of the coil spring.

Other aspects of the invention are achieved as follows:

A serpentine belt drive system for an automotive vehicle comprising adrive assembly including an internal combustion engine having an outputshaft with a driving pulley thereon rotatable about a driving pulleyaxis, a sequence of driven assemblies each having a driven pulleyrotatable about an axis parallel with the driving pulley axis and aserpentine belt mounted in cooperating relation with the driving pulleyand with the driven pulleys in a sequence which corresponds with thesequence of the driven assemblies when related to the direction ofmovement of the belt to cause the driven pulleys to rotate in responseto the rotation of the driving pulley, the sequence of driven assembliesincluding an alternator assembly including a housing and an armatureassembly mounted in the housing for rotation about an armature axis; ahub structure fixedly carried by the armature assembly outwardly of thehousing for rotation therewith about the armature axis, an alternatorpulley is mounted on the hub structure for rotational movement withrespect to the hub structure about the armature axis; an outer springengaging structure disposed between the alternator pulley and the coilspring, the outer spring engaging structure engaging volutes of the coilspring as a result of radial expansion of the coil spring; and a coilspring resiliently coupling the alternator pulley with the hubstructure, the coil spring transmitting the driven rotational movementsof the alternator pulley by the serpentine belt to the hub structuressuch that the armature assembly is rotated in the same direction as thealternator pulley while being capable of instantaneous relativerotational movements in opposite directions with respect to thealternator pulley during the driven rotational movement thereof, anouter spring engaging structure disposed between the alternator pulleyand the coil spring, the outer spring engaging structure engagingvolutes of the coil spring as a result of radial expansion of the coilspring.

A serpentine belt drive system for an automotive vehicle comprising adrive assembly including an internal combustion engine having an outputshaft with a driving pulley thereon rotatable about a driving pulleyaxis, a sequence of driven assemblies each having a driven pulleyrotatable about an axis parallel with the driving pulley axis and aserpentine belt mounted in cooperating relation with the driving pulleyand with the driven pulleys in a sequence which corresponds with thesequence of the driven assemblies when related to the direction ofmovement of the belt to cause the driven pulleys to rotate in responseto the rotation of the driving pulley, the sequence of driven assembliesincluding an alternator assembly including a housing and an armatureassembly mounted in the housing for rotation about an armature axis; ahub structure fixedly carried by the armature assembly outwardly of thehousing for rotation therewith about the armature axis, an alternatorpulley mounted on the hub structure for rotational movement about thearmature axis; a coil spring resiliently coupling the alternator pulleywith the hub structure, the coil spring transmitting the drivenrotational movements of the alternator pulley by the serpentine belt tothe hub structure such that the armature assembly is rotated in the samedirection as the alternator pulley while being capable of instantaneousrelative rotational movements in opposite directions with respect to thealternator pulley during the driven rotational movement thereof, thealternator pulley being mounted for axial movement relative to the hub,the coil spring axially expanding during radial contraction thereof andthereby applying an increasing axial damping force on the pulley so asto dampen rotational movement of the pulley relative to the hubstructure.

A decoupler has a hub structure capable of being mounted on a shaft; apulley mounted on the hub structure and capable of relative rotationalmovement with respect to the hub structure; a coil spring resilientlycoupling the pulley with the hub structure, the coil spring capable oftransmitting driven rotational movements of the pulley to the hubstructure; an inner spring engaging structure rotationally fixed withrespect to the pulley and engaging volutes of the coil spring as aresult of radial contraction of the coil spring.

A decoupler has a hub structure capable of being mounted on a shaft; apulley mounted on the hub structure and capable of relative rotationalmovement with respect to the hub structure; a coil spring resilientlycoupling the pulley with the hub structure, the coil spring capable oftransmitting driven rotational movements of the pulley to the hubstructure; an outer spring engaging structure disposed between thealternator pulley and the coil spring, the outer spring engagingstructure engaging volutes of the coil spring as a result of radialexpansion of the coil spring.

A decoupler has a hub structure capable of being mounted on a shaft; apulley mounted on the hub structure and capable of relative rotationalmovement with respect to the hub structure; a coil spring resilientlycoupling the pulley with the hub structure, the coil spring capable oftransmitting driven rotational movements of the pulley to the hubstructure; the pulley being mounted for axial movement relative to thehub structure; and the coil spring axially expanding during radialcontraction thereof and thereby applying an increasing axial dampingforce on the pulley so as to dampen rotational movement of the pulleyrelative to the hub structure. dr

DESCRIPTION OF THE DRAWINGS

The present invention is further described in the detailed descriptionwhich follows, by reference to the noted drawings by way of non-limitingexemplary embodiments, in which like reference numerals representsimilar parts throughout the several views of the drawings, and wherein:

FIG. 1 is a front elevational view of an automobile internal combustionengine having a serpentine drive system embodying the principles of thepresent invention connected therewith;

FIG. 2 is an enlarged fragmentary sectional view of the first embodimentof the isolator device taken along the line 2—2 of FIG. 1;

FIG. 3 is an enlarged fragmentary sectional view of an alternateembodiment of a mounting arrangement of the alternator pulley to the hubstructure;

FIG. 4 is an enlarged fragmentary sectional view showing an alternateembodiment having a coil spring with varying diameter coils; and

FIG. 5 is an enlarged fragmentary sectional view showing an alternateembodiment of the isolator device of the present invention.

DETAILED DESCRIPTION

Referring now more particularly to the drawings, there is shown in FIG.1 an automotive internal combustion engine, generally indicated at 10,which includes a schematically indicated engine frame 12 and an outputshaft 14. Fixed to the output shaft 14 is a driving pulley 16 formingpart of a serpentine drive system, generally indicated at 18. The drivesystem 18 includes an endless belt 20. The belt 20 is of the thinflexible type, as, for example, a poly-V belt. The belt 20 is trainedabout the driving pulley 16 and a sequence of driven pulley assemblies22, 24, 26, 28, and 30, each of which is fixed to a respective shaft 32,34, 36, 38, and 40. Except for the pulley assembly 22, which is a simpleidler pulley, the shafts are connected to operate various engine orvehicle accessories. For example, shaft 34 drives an engine water pump,shaft 36 an electrical alternator, shaft 38 an electromagnetic clutch ofa compressor for an air-conditioning system for the automobile, andshaft 40 an oil pump of the power steering system.

It will be understood that the internal combustion engine 10 may be ofany known construction. In accordance with conventional practice, theoperation of the engine is such as to impart vibratory forces to theengine frame 12. All of the accessories are mounted on the engine frame12 so that the shafts are rotated about parallel axes which are fixedwith respect to the engine frame 12 and parallel with the output shaft14 thereof. The belt 20 is tensioned by a belt tensioner, generallyindicated at 42 which may be of any construction. However, a preferredembodiment is the tensioner disclosed in commonly assigned U.S. Pat. No.4,473,362, the disclosure of which is hereby incorporated by referenceinto the present specification.

As shown, the belt tensioner 42 includes an idler pulley 44 which isdisposed in rolling engagement with the flat back surface of the belt20, the tensioner pulley being spring biased to maintain a generallyconstant tension in the belt 20.

As best shown in FIG. 2, the present invention is more particularlyconcerned with the functional connection between the pulley, generallyindicated at 26, and the shaft 36 of the alternator. The alternatorincludes a housing 46 within which the armature assembly, generallyindicated at 48, is journalled, as by bearings 50. As shown, alternatorshaft 36 forms a part of the armature assembly 48 and includes an endportion extending outwardly of the alternator housing 46.

The pulley 26 forms part of a coupling assembly 29, which is mounted onthe shaft 36, for coupling the belt 20 to the shaft 36. Couplingassembly 29 also includes, among other elements, the hub structure,generally indicated at 52, which is fixed to the outwardly extending endof the alternator shaft 36. As shown, the hub structure 52 includes aninner sleeve portion 54 which, in the illustrated embodiment, extendsover the end of the alternator shaft 36 end portion. In otherembodiments, depending on the alternator and pulley geometry, the innersleeve portion 54 may not extend over the end of the alternator shaft 36end portion. As shown, the extremity of the shaft 36 is threaded asindicated at 56 and the sleeve 54 is formed with a series of interiorthreads 58 which are disposed in meshing relation with the threads onthe end of the shaft 36. The inner surface 53 of the hub structure 52 atthe outer axial end 60 thereof may be formed of a inner toothed sprocketfor receiving a correspondingly configured tool to rotate the hub 52onto the shaft for threadedly securing the hub structure 52 on the shaft36. Alternatively, the annular end surface 60 may be formed to provide ahexagonal socket for receiving a tool for securing the sleeve 54 overthe shaft 36 by relative rotation between the sleeve 54 and shaft 36, asknown in the art. It can be seen that as the sleeve portion 54 isthreaded on the end of the shaft 36, the axially inner end surfacethereof is squeezed one side of the inner race of the ball bearing 50against a flange 64 on the shaft 36 and the other side of the inner raceof the ball bearing 50 with the inner race of a ball bearing 50 mountedon the shaft 36 in abutting relation with the ball bearing 50.

As best shown in FIG. 2, the alternator pulley 26 includes an annularpulley member 68 having an exterior poly-V surface 70 for rollinglyengaging the operative poly-V side of the serpentine belt 20. One end ofthe annular pulley member 68 has axial flange 72, which includes aradially inwardly extending portion 71 and then an axially extendingportion 73 as shown. Flange 72 may also include a radially outwardlyextending end portion 75 as shown. The inner surface 69 of the flange 72is disposed in engagement with an L-shaped, annular bushing or bearing78. The annular bushing 78 is preferably an integral structure having anaxial extending portion 79 having a radially outer surface disposed inengagement with an portion 73 of flange 72, and a radially inner surfacedisposed in engagement with a contact surface 80 at the end of the hubstructure 52. The annular bushing 78 preferably also includes a radialextending portion 128 having an axially outer surface disposed inengagement with radially inwardly extending portion 71 of the flangeportion 72, and an axially inner surface thereof disposed in engagementwith a radially outwardly extending portion 57 of hub structure 52 asdescribed below. Although the annular bushing 78 is shown as an integralstructure, the annular bushing may also include separate structures: anaxial portion, corresponding to axial portion 79, and a radial portion,corresponding to radial portion 128. The annular bushing 78 supportsrelative motion between the pulley 26 and the shaft 36. The annularbushing 78 may be made of a material having a low coefficient offriction to facilitate sliding action between the pulley 26 and the hub52. For example, the annular bushing 78 may be a polymeric material. Thematerial of the annular bushing 78 may also a metal, such as brass, or alead-alloy. A lubricant may also be used at the interface between theannular bushing 78 and pulley 26 to facilitate sliding contacttherebetween. The bushing 78 may be fixed relative to one of the hub 52or pulley 26, or may be movable (slidable) with respect to both.Alternatively, as shown in FIG. 3, rather than using annular bushing 78,a ball bearing 77 may be disposed between the flange portion 72 and thecontact surface 80 of the hub structure 52 to support the relativemotion between the pulley 26 and the hub 52. In such a configuration, athrust washer 127 is utilized in place of the radial portion 128 of theannular bushing 78 between the radially inwardly extending portion 71 ofthe pulley and the protruding portion 57 of the hub 52.

The hub structure 52 includes the forementioned radially protrudingportion 57 (hereinafter referred to as the radial portion 57) and anaxially inwardly extending portion 59 integrally formed thereon. In theillustrated embodiment, the portion 59 extends axially from the end ofthe radial portion 57 toward the alternator assembly 46. Alternatively,the orientation of the portion 59 and radial portion 57 may be reversedto permit the poly-V surface 70 of the annular pulley member 68 to belocated closer to or further away from the alternator housing. Aclearance gap G4 is maintained between the inner surface 84 of thepulley 26 and the outer surface 63 of the axial portion 59 of the hubstructure 52 so that the pulley rotates freely thereabout. It can beseen that the mounting of the pulley 26 with respect to the hubstructure 52 is such as to define an annular space 86 therebetween,generally defined by the pulley 26, the sleeve portion 54 and radial 57portion of the hub structure. Disposed within this annular space 86,between an inner surface 84 of the pulley 26 and the outer surface 88 ofthe hub structure 52, is a spring retaining member made of low carbonsteel, generally indicated at 92. The spring retaining member 92(hereinafter referred to as the spring retainer 92) is formed of anannular cylindrical inner portion 96 and an annular cylindrical outerportion 100 connected by a radial wall portion 104. An exteriorcylindrical surface 108 of the outer portion 100 frictionally engagesthe cylindrical interior surface portion 74 of the pulley 27, via apress-fit, for example, to form a rigid connection therebetween. Asecond annular radial bushing 112 is disposed between the inner surface116 of the inner portion 96 of spring retainer 92 and the outer surface88 of the sleeve portion 54 of the hub structure 52. Bushing 112includes a flange 113 disposed at one end. Specifically, bushing 112 ispress-fit to retainer 92 and is thus fixed to spring retainer 92. Thesecond radial bushing 112 further supports the relative motion betweenthe pulley 26 (via spring retainer 92) and the hub structure 52. Theradial bushing 112 may be made of a material having a low coefficient offriction to facilitate sliding action between the spring retainer 92 andthe hub 52. For example, the radial bushing 112 is preferably made froma steel material with teflon bonded on an inner surface thereof thatengages sleeve 54. The material of the radial bushing 112 may also ametal, such as brass, or a lead-alloy. A lubricant may also be used atthe interface between the second radial bushing 112 and inner portion 96of the sleeve retainer 92 to facilitate sliding contact therebetween.The flange 113 is generally made of the same material as the bushing112, and a lubricant may also be used at its interface with the hubstructure 52, such that a low friction surface is provided for the hubstructure 52 to contact should the pulley 26 move axially duringoperation, e.g., in the case of a pulley misalignment.

The pulley 26 is interconnected with the hub structure 52 by a generallyhelical spring 118 mounted within the annular space 86. The spring 118is disposed in surrounding relation to the inner portion 96 of thespring retainer 92, and is radially separated from the main coilsthereof by a clearance gap GI when no torque is applied thereto (i.e.,when at rest). While not shown, it can be appreciated by those skilledin the art that the spring 118 in the illustrated embodiment has one endbent axially outwardly, and this end extends within a notch formed inthe radial portion 57 of the hub structure 52 in order to fit one end ofspring 118 to the hub structure 52. The opposite end of the spring 118is bent to extend axially inwardly, and this end is engaged within anotch formed in the wall portion 104 of the spring retainer 92.Alternatively, a spring without a bent end could be engaged by pressfitting it into the radial portion 57 of the hub structure 52. Althougha spring 118 is shown in the illustrated embodiment which hasrectangular cross-sectioned volutes, a coil spring may also be usedwhich has circular cross-sectional volutes.

Disposed between the spring 118 and the pulley 26 and adjacent the outerportion 100 of the spring retainer 92 is at least one spring sleeve 105.The sleeve is preferably not a complete cylindrical configuration, butis split so as to provide a “C”-shaped configuration allowing it toexpand and contract radially. If one spring sleeve 105 is used, it mayextend the entire length between the outer portion 100 and the end 61 ofthe axial portion 59 of the hub structure (a clearance gap is, ofcourse, maintained between each end of the spring sleeve 105 and thespring retainer and axial portion 59), thus covering a majority of thevolutes of the spring 118. Alternatively, the at least one spring sleeve105 may include a plurality of spring sleeves 105 disposed adjacent toeach other. The outer diameter surface 134 of the spring 118 and theinner diameter surface 135 of the sleeve 105 is such that a clearancegap G2 is formed therebetween when no torque is applied to the spring(when the system is at rest). Alternatively, the clearance gap G2 mayexist between the spring sleeve 105 and the inner surface 86 of thepulley 26, depending on the particular fit of the spring sleeve 105around the spring 118. The spring sleeve 105 is preferably made of amaterial having a low coefficient of friction to facilitate slidingcontact of the spring 118 against the sleeve 105 when the spring expandsinto contact with sleeve 105. For example, the spring sleeve 105 ispreferably a nylon material. The material of the spring sleeve 105 mayalso a metal, such as brass, or a lead-alloy. In FIG. 2, a spring slipring 106 is also illustrated, disposed on a portion of the retainer 92proximate to the hub end of the spring 118. The spring slip ring 106 hasa “C”-shaped configuration similar to that of the spring sleeve 105 andperforms essentially the same function as the spring sleeve 105 in aradially spring-constricting direction, providing a low-frictionsliding-contact surface between the retainer 92 and the spring 118 whenthe spring 118 constricts against the retainer 92. The spring slip ring106 may be made of the same material as the spring sleeve 105, and mayor may not extend the entire length of the spring. Typically, if thespring slip ring 106 does not extend the full length of the spring 118,it is positioned proximate to the hub end of the spring, as the hub endis usually the first portion of the spring 118 to deflect under load.

The spring 118 may be installed within the annular space 86 in anaxially compressed state, between radially extending walls 57 and 104.In order to support the spring 118 in this state, a spring support 125is provided in the retainer 92, resting against retainer surface 104.The spring support is held in position by a tab that engages the samenotch in the retainer 92 that is used to secure the spring 118. Thespring support 125 is made of a low friction material such as nylon, andis contoured to follow the shape of the end surface of the installed,compressed spring 118. In general, the spring support 125 maintainsparallel coil alignment of the spring 118 once it is installed.

The wall 57 is axially fixed, as the hub is fixed to shaft 36. The wall104 of the retainer 92 receives the axial load, which in turn istransmitted to pulley 26 as a result of the fixed connection betweenpulley 26 and retainer 92. Thus, the retainer 92 and pulley,26 arebiased towards the left in FIG. 2 under the force of spring 118. Thishas the effect of axially compressing the radial portion 128 of theannular bushing between pulley 26 (wall 71 thereof) and the hubstructure 52 (wall 57 thereof).

The presence of this axial load is used as a source of torsional dampingof the isolator device, which moderates the pulley 26 and hub structure52 velocity differential caused by torsional inputs from the engine. Theamount of torsional damping may be engineered by adjusting the axialspring rate of spring 118. The torsional damping is enabled to somedegree as a result of the ability of the pulley to move slightly axiallyunder the load of spring 118 through sliding engagement of the tefloncoated surface of radial bushing 112 on hub sleeve 54. The press-fitinsertion of spring retainer 92 against the surface portion 74 of thepulley 26 is the last step in the assembly of coupling assembly 29, andaxially retains all components within the assembly 29.

The level of torsional damping is designed to increase with increasingapplication of torque. That is, as a positive torque is applied to thespring 118 as a result of the pulley 26 being driven by belt 20, innerdiameter 130 of the spring 118 decreases, resulting in an increase inspring length. In other words, as the coils radially tighten towards theshaft axis as a result of the pulley 26 being driven, the coils are alsocaused to expand axially. This increase in length, in turn, causes anincrease in the axial load reacting against the radial portion 128 ofbushing 78, thus damping in movement between pulley 26 and hub 52. Atthe same time, as the torque increases, the diameter of the wire spring118 decreases until the point where its inner diameter 130 contacts theouter surface 98 of the inner portion 96 of the spring retainer 92,which causes a sharp increase in spring rate of spring 118. Thissignificantly limits further deflection of the spring in the radiallyinward and axially outward directions. For example, and not intended tobe limiting, the spring rate of spring 118 has been shown to increasefrom about 0.4 Nm/deg prior to contacting the spring retainer 92 to morethan 3 Nm/deg after contacting the spring retainer 92. The amount ofradially inward deflection of the wire spring 118 can be varied byengineering the clearance gap G1 between the inner diameter 130 of thewire spring 18 and the spring retainer's 92 inner ring outer diameter98. Though not intended to be limiting, the system may be engineeredsuch that between about 25–35 degrees, (in one preferred example 30degrees) of positive rotational movement of the pulley 26 relative tohub 52 is established (relative to the at-rest position) before contactis made by the spring 118 with the inner portion 96 of the springretainer 92.

It will be understood by those skilled in the art during most dynamicoperating conditions there are substantially very low loads on thespring 118, and the spring is generally not in contact with the innerportion 96 of the spring retainer or the spring sleeve 105. In general,the spring 118 is caused to contact the inner portion 96 of the springretainer only during abrupt system changes such as during enginestart-up. It is during such abrupt changes during start-up that thespring 118 would undergo the most torsional stress, for example in theaforementioned U.S. Pat. No. 5,139,463.

Of course, after this initial spring radial contraction, an oppositerecoiling force will exist, as a result of the shaft accelerationmomentarily exceeding that of the pulley, thus causing relativelysignificant expansion of the spring 118, until the outer diameter of thespring 118 contacts the inner surface 135 of spring sleeve 105, againsuch contact having the result of increasing the spring rate.

The amount of expansion is controlled by the clearance gap G2 betweenthe outer diameter 134 of the spring 118 and the inner diameter 135 ofthe spring sleeve 105. Preferably, this reverse travel (i.e., negative,expansion direction) of the spring 118 is limited to be much less thanthat of the forward direction (i.e., positive, contraction direction) toreduce the stress in the spring 118 and improve component durability.For example, though not intended to be limiting, the spring may be sizedsuch that 5–10 degrees of negative rotational movement of the pulley 26relative to the hub 52 (with respect to the relative angular positionswhen the system is at rest) is achieved before sufficient springexpansion causes contact to be made with the spring sleeve 105. In theabsence of this travel control (both in the positive and negativedirections) the spring 118 could potentially be subject to largedisplacements which may result in fatigue of the spring.

Though not intended to be limiting, during an engine start-up, thespring may behave as follows. The wire spring 118 may contract andcontact the inner portion 96 of the spring retainer 92, and then expandto contact the spring sleeve 105. The wire spring 118 may repeat theabove motion at least once more before the applied torque in the springdiminishes and the spring 118 does not contact either the inner portion96 or the spring sleeve 105 to achieve steady dynamic state.

The axial load in the spring 118 applied to portion 128 of bushing 78also helps to slow the relative motion between the hub structure 52 andthe pulley before spring 118 contact is made in either direction, whichthus dissipates some energy as heat, rather than absorbing this energyin the spring 118.

Before the spring 118 deflection is limited in either direction bycontacting the spring retainer 92 (in the positive direction) or springsleeve 105 (in the negative direction), the clearance gaps G1 and G2must first be taken-up by the spring. When the spring 118 contracts tocontact the spring retainer 92, the spring 118 exhibits a significantincrease in its spring rate. Likewise, a significant increase in springrate is realized when the spring 118 expands so that the outer diameter134 of the spring 118 contacts the sleeve 105. In this manner, a spring“soft stop” is created, as opposed to a solid contact between the pulley26 and hub structure 52, when relative rotation therebetween reaches apredetermined level.

In the above embodiment, the pulley 26 is interconnected to the hubstructure 52 by the coil spring 118, and spring retainer 92. When thereis a positive torque transmitted by the belt 20 to the pulley 26, therotational movement of the pulley 26 will be imparted to the hubstructure 52 and, hence, the entire armature assembly 48 of thealternator, through the coil spring 118. During normal operation of theengine (i.e., after start-up), the resiliency of the coil spring 118enables the alternator armature assembly 48 under these circumstances tohave instantaneous rotational movements with respect to the pulley 26 soas to accommodate the high inertia characteristics of the alternatorarmature assembly 48. Similarly, where negative torques are imparted tothe pulley 26 by the belt 20, instantaneous relative motion of thealternator armature assembly 48 with respect to the pulley 26 isaccommodated so that any tendency for the belt 20 to slip with respectto the pulley 26 due to changes in torque in the belt 20 and the highinertia of the alternator armature assembly 48 are generallyaccommodated so as to minimize belt slippage.

For the purposes of this disclosure, the portion 96 of the springretainer 92 between the spring 118 and hub 54 may be termed as an innerspring engaging structure, while the sleeve 105 may be termed on outerspring engaging structure.

It will be understood that the characteristics of the spring 118 aretuned to the particular drive system and more particularly to theparticular characteristic of the engine of the drive system. Thestrength of the spring 118 is determined by diameter dimension of thesteel utilized to form the coil. Proper tuning is determined by thespring rate which is a function of the number of turns or volutesincluded between the spring ends 121 and 123.

Although not shown in FIG. 2, it will be appreciated that a cap may beinstalled over the exposed end of the pulley 26 once the couplingassembly 29 has been installed to protect the internal components of thecoupling assembly 29 from contamination. The cap may, for example, becomprised of an injection-molded plastic material.

In an alternative embodiment, the spring 118 may be constructed suchthat each successive volute is decreasing in inner and outer diameter130, 134 (shown in FIG. 4). With this configuration, as positive torqueis applied to the spring, the spring 118 volutes contact the outerdiameter of the inner portion 96 of the spring retainer 92 in successivemanner, which results in a progressive rising rate in spring stiffness.Similarly, as negative torque is applied, the spring 118 volutes contactthe inner cylindrical surface of the spring sleeve 105 in successivemanner, causing a progressive rising rate in spring stiffness.

FIG. 5. shows another embodiment of the decoupler, which is generallyindicated as numeral 229. In this embodiment, the end 260 of the hubstructure 252 radially extends for engagement with the corresponding end228 of the pulley 226. An annular, radial bushing 278 may be disposedbetween the end 260 of the hub structure 252 and the end 228 of thepulley for facilitating sliding contact therebetween. The radial bushing278 is of the same material as that described of bushing 78 in theprevious embodiment, and a lubricant may be applied thereto. The bushing278 may include a protruding tab 281 for engagement with an indentation273 formed in the contact surface 277 of the pulley 226 for fixing theaxial position of the radial bushing 278. It can be appreciated that theprotruding tab 281 may be formed on an opposite side of the radialbushing 278 for engagement with an indentation (not shown) formed in thehub structure 252.

As seen in FIG. 5, the axial load of the spring 118 (which is installedas described above in the previous embodiment) is received by a thrustwasher 229 on the opposite side of the spring 118, compared with theFIG. 2 embodiment] In this embodiment, a rigid spacer 266 and the thrustwasher 229 are disposed between the decoupler 229 and the alternatorassembly 46. As will be understood by those skilled in the art, aportion of the axial load of the spring 118 is also taken up by the hubstructure 52 by the bearing contact of the pulley 226 via the radialbushing 278. An inner portion of the spacer 266 is axially squeezedbetween the hub 252 and the inner race of a ball bearing assembly 50 ofthe alternator assembly 46. The thrust washer 229 is disposed betweenthe back side of connecting wall portion 104 and a flange portion 267 ofthe rigid spacer 266. The thrust washer 229 may be made of the same lowcoefficient of friction material as the annular bushing 78 of theprevious embodiment, and the thrust washer supports relative motionbetween the shaft 36 and the pulley 226. Though the spring 118 in FIG. 5is shown as having varying diameter coils, the diameter of the coils maybe substantially the same, as with the first embodiment. The interactionbetween the spring 118 and other components of the decoupler 229 is thesame as that described in the first embodiment.

Although the present discussion herein and throughout describes thedecoupler 29 as being mounted to an alternator, it will be understood bythose skilled in the art that the decoupler of the present invention canbe mounted on any other similar device.

While the invention has been described with reference to the certainillustrated embodiments, the words which have been used herein are wordsof description, rather than words or limitation. Changes may be made,within the purview of the appended claims, without departing from thescope and spirit of the invention in its aspects. Although the inventionhas been described herein with reference to particular structures, acts,and materials, the invention is not to be limited to the particularsdisclosed, but rather extends to all equivalent structures, acts, andmaterials, such as are within the scope of the appended claims.

1. A decoupler, comprising: a hub structure capable of being mounted ona shaft; a pulley mounted on said hub structure and capable of relativerotational movement with respect to said hub structure; a coil springextending between said pulley and said hub structure resilientlycoupling said pulley with said hub structure, said coil springtransmitting driven rotational movements of said pulley to said hubstructure; an inner spring engaging structure comprising a slip ring incontact with a portion of said coil spring and rotatably mounted on saidhub structure and rotationally fixed with respect to said pulley, saidinner spring engaging structure engaging volutes of said coil spring asa result of radial contraction of said coil spring, whereby as said coilspring engages said inner spring engaging structure, a spring rate ofsaid coil spring increases before directly coupling said pulley to saidhub structure; a C-shaped sleeve surrounding said coil spring saidsleeve limiting radial expansion of said coil spring, whereby as saidcoil spring engages said sleeve, said spring rate increases beforedirectly coupling said pulley to said hub structure; and wherein saidcoil spring is radially spaced from said inner spring engaging structureby a first predetermined clearance gap and said sleeve is radiallyspaced from said pulley by a second predetermined clearance gap.
 2. Adecoupler according to claim 1, wherein said first clearance gap enablesa first range of movement in a first direction of said pulley relativeto said hub structure of between about 25 to 35 degrees.
 3. A decoupleraccording to claim 2, wherein said first range of movement is about 30degrees.
 4. A decoupler according to claim 2, wherein said secondclearance gap enables a second range of movement in second direction,opposite to said first direction, of said pulley relative to said hubstructure of between about 5 to 10 degrees.
 5. A decoupler according toclaim 4, wherein said first range of movement is about 30 degrees.
 6. Adecoupler according to claim 1, wherein said second clearance gapenables a second range of movement of said pulley relative to said hubstructure of between about 5 to 10 degrees.
 7. A decoupler according toclaim 1 wherein said spring rate increases from about 0.4 Nm/deg toabout 3 Nm/deg.
 8. A decoupler according to claim 1, wherein said slipring is positioned proximate an end of said coil spring that deflectsfirst under load.
 9. A decoupler according to claim 1, wherein said coilspring is constructed having successive volutes of decreasing inner andouter diameter.
 10. A decoupler according to claim 8, wherein said slipring and said sleeve are made of a material having a low coefficient offriction to facilitate sliding contact with said coil spring.
 11. Adecoupler comprising: a hub structure capable of being mounted on ashaft; a pulley mounted on said hub structure and capable of relativerotational movement with respect to said hub structure; a coil springextending between said pulley and said hub structure resilientlycoupling said pulley with said hub structure, said coil springtransmitting driven rotational movements of said pulley to said hubstructure; an inner spring engaging structure rotatably mounted on saidhub structure and rotationally fixed with respect to said pulley, saidinner spring engaging structure engaging volutes of said coil spring asa result of radial contraction of said coil spring, whereby as said coilspring engages said inner spring engaging structure, a spring rate ofsaid coil spring increases before directly coupling said pulley to saidhub structure, wherein said inner spring engaging structure comprises aradial wall portion connected to said pulley, and said radial wallportion being connected to said spring; and wherein said hub structurehas a radial portion connected to said spring, said radial portionfrictionally engaging said pulley, whereby radial contraction andexpansion of said spring urges said radial portion out of and intofrictional engagement with said pulley, respectively, generating aproportional damping force moderating velocity differences between saidhub structure and said pulley.
 12. A decoupler according to claim 11,wherein said hub structure has a sleeve portion configured to extendover said shaft and said inner spring engaging structure is journalmounted on said sleeve portion by a bushing.
 13. A decoupler accordingto claim 12, wherein said pulley is journal mounted on said hubstructure by an annular bushing.
 14. A decoupler according to claim 13,wherein said annular bushing has a radial portion extending between saidradial portion of said hub structure and said pulley.